The present invention relates generally to fiber-reinforced resin structures, and more particularly to a process for optimizing resin distribution with the incorporation of a grooved core integral to the fiber-reinforced resin structure.
Vacuum assisted resin transfer molding (VARTM) and related processes and techniques have been widely used to fabricate relatively large fiber-reinforced composite articles. Such articles may include coach chassis for buses and trailers and fiber glass boat hulls, for example.
In general, the VARTM process includes the distribution of dry, fiber strips, plies or mats about the surface of a female mold to form a fiber lay-up of a desired thickness. The fiber strips or plies may take the form of a cloth or sheet of fibers of glass, carbon or other suitable material. In addition, one or more rigid core layers may be included. The core layers may be formed of a solid foam material or balsa wood. The core layers may be sandwiched between the fiber plies to form a fiber/core composite lay-up or laminate.
A flexible, fluid impermeable bag, sheet or covering is positioned atop the exposed lay-up and sealed about the periphery thereof. A relative vacuum is drawn between the mold and the bag, thereby causing the bag to compress against the fiber lay-up. A chemically catalyzed liquid resin is introduced into the evacuated bagged mold through a series of resin supply lines or conduits. A multitude of individual resin supply lines may be used so as to facilitate distributed wetting or infusion of the liquid resin about the fiber lay-up. The vacuum source and resin supply lines are strategically positioned relative to one another in a manner which encourages controlled wetting. In this respect, the vacuum source may be applied at one side of the fiber lay-up and the resin introduced at an opposing side, and thus tending to cause the resin to be pulled across and wet portions of the fiber lay-up therebetween.
Underwetting and overwetting of the fiber lay-up are particularly problematic, as such conditions may result unacceptable structural weaknesses and deficiencies of the resultant article. In addition, nonuniform resin distribution may also result unacceptable structural weaknesses and deficiencies of the resultant article.
Contemporary techniques for facilitating more uniformed or homogeneous resin distribution include the use of cloth material adjacent the fiber lay-up. The cloth forms a screen or matrix of open spaces which tends to wick the resin, and thereby facilitates resin flow. The cloth is removed or peeled away prior to the resin fully curing. Other techniques for enhancing more uniformed resin distribution focus on the resin delivery apparatus, such as specially formed resin supply conduit manifolds and manifolds which are integrated into the vacuum bag itself. While these and other techniques enhance the distribution of resin about the fiber lay-up, they each require the positioning and application of a particular type of cloth or conduit manifold or the like, each time the article is formed. In addition, specialized procedures for disposal and/or clean-up of such additional apparatus must be addressed as well. As such, use of such apparatus increases the time and skill requirements in order to fabricate a resultant article to desired quality control standards.
Where resin overwetting is detected prior to the resin curing, excess resin may be removed via skilled labor intensive steps. Where underwetting is detected in a cured lay-up, the structure may be required to undergo additional processing in the form of reinfusion of liquid resin and subsequent curing of the resin. While such labor intensive steps, including inspection tasks, may be result in a structure which conforms to desired mechanical requirements, such a process so limits the production efficiency so as to make the process economically nonfeasible.
As such, based upon the foregoing, there exists a need in the art for an improved method and device, for enhancing resin distribution in comparison to the prior art.
In accordance with the present invention, there is provided a process for optimizing resin distribution during VARTM fabrication of a fiber-reinforced resin structure having a core body having a core upper surface extending between first and second edges, and at least one ply disposed upon the core upper surface. A resin infusion port is formed along the first edge for dispensing resin thereat. A vacuum application port is formed along the second edge for drawing a vacuum thereat. Extending along the core upper surface between the first and second edges is a longitudinal resin flow axis. Longitudinal resin distribution grooves are formed along the core upper surface substantially parallel to the longitudinal resin flow axis. Lateral resin distribution grooves are formed along the core upper surface. The lateral resin distribution grooves are arrayed to intersect the longitudinal resin distribution grooves. At least one fiber-reinforced ply is applied upon the grooved core upper surface. A vacuum is drawn between the resin infusion and the vacuum application ports. Resin is dispensed at the resin infusion port. The longitudinal and lateral resin distribution grooves are formed to wet the fiber-reinforced ply at substantially equal ply resin wetting rates in directions along the longitudinal resin flow axis and perpendicular thereto.
Preferably, the longitudinal and lateral resin distribution grooves are cooperatively formed and spaced to migrate the resin to the second edge upon substantially wetting the fiber-reinforced ply between the longitudinal resin distribution grooves. In this respect, the lateral resin distribution grooves may have a spacing which is a function of resin viscosity and ply wetability.
The process of fabricating fiber-reinforced structures in accordance with the present invention presents numerous advantages not found in the related prior art. In this respect, the process is particularly adapted to provide enhanced resin distribution by the incorporation of the cooperatively formed longitudinal and lateral resin distribution grooves. Such enhanced resin distribution tends to increase the structural integrity of the resultant fiber-reinforced resin structures and reduce the time and skill fabrication requirements. This is because the longitudinal and lateral resin distribution grooves are sized and spaced for optimum resin distribution, i.e., the longitudinal and lateral ply wetting rate are substantially equal. As such, the resultant structures can be produced at rates which make the technology more economically viable.
As such, the present invention represents an advance in the art.